Nervous Systems Nervous Systems Evolution of the Nervous
- Slides: 76
Nervous Systems
Nervous Systems
Evolution of the Nervous System • Nerve Net – Cnidarian, Ctenophora • Nerve Ring with radial nerves – Echinodermata • Bilateral Nervous Systems – Cephalization (ganglia or brain) – Nerve cord
Evolution of the Nervous System • Bilateral Nervous Systems – Ganglia and two or more longitudinal nerve cords • platyhelminthes, some mollusca – Ganglia (brain) and ventral nerve cord • annelida, arthropoda, some mollusca – Brain and dorsal nerve cord • chordata
Overview of a Nervous System
Overview of a Nervous System • Sensory Input – conduction of signals from sensory receptors – PNS • Integration – environmental information is interpreted – CNS (brain and spinal cord) • Motor Output – conduction of signals to effector cells – PNS
Neurons
Neurons • Cell body – nucleus and organelles • Dendrites – short and branched – toward cell body • Axons – long and unbranched – away from cell body
Axons • Myelin Sheath - insulating layer • Node of Ranvier - gaps between Schwann Cells • Synaptic Terminals - neuron ending
Clusters of Neurons • Ganglion – Cluster of nerve cell bodies in the PNS • Nuclei – Cluster of cells in the brain
Supporting Cells • Glia (glue) – Astrocytes (structural support) • Creates tight junctions and forms the blood-brain barrier – Radial Glia • Form tracks for new neurons formed in the neural tube – Oligodendrocytes • Form myelin sheath in brain – Schwann Cells • Form myelin sheath in the PNS
Reflex • Sensory neuron to a motor neuron
Neural Signals • Membrane Potential • Sodium-Potassium Pump
Threshold Potential
Resting State • Both sodium and potassium activation gates are closed • Interior of cell is negative
Depolarization State • Sodium activation gates are opened on some channels • Interior of cell becomes more positive
Rising Phase of Action Potential • Most sodium activation gates are opened • Potassium activation gates are still closed
Falling Phase of Action Potential • Inactivation gates on sodium channels are closing • Activation gates on potassium channels are opened • interior of cell becomes more negative
Undershoot • Both gates to sodium channels are closed • Potassium channels are closing • Membrane returns to its resting state
Propagation of the Action Potential • Localized event • First action potential’s depolarization sets off second action potential • Travels in one direction due to refractory period
Salatory Conduction • Action Potential jumps from node to node • Speeds up signal from 5 m/sec to 150 m/sec
Communication Between Synapses • Electrical Synapses – gap junctions allow for direct transfer of action potential (used during escape responses) • Chemical Synapses – uses neurotransmitters
Chemical Synapse
Chemical Synapses • Action potential triggers an influx of calcium • Synaptic vesicles fuse with presynaptic membrane • Neurotransmitter released into synaptic cleft • Neurotransmitters bind to receptors and open ion channels on postsynaptic membrane which sets off new action potential • Neurotransmitters are degraded by enzymes or removed by a synaptic terminal
Neurotransmitters
Postsynaptic Potentials
Postsynaptic Potentials • Subthreshold – doesn’t reach threshold • Temporal Summation – two signals do not reach threshold level but occur close enough to set off action potential • Spatial Summation – two signals are set off at the same time setting off an action potential • Spatial Summation with an inhibitor – doesn’t reach threshold
Vertebrate Nervous System
Central Nervous System • Ventricles (4) – Cerebrospinal fluid • White Matter – Made up of axons • Gray Matter – Made up of dendrites
Peripheral Nervous System
Peripheral Nervous System • Autonomic Nervous System regulates the internal environment (usually involuntary) • Somatic Nervous System regulates the external environment (usually voluntary)
Autonomic Nervous System
Autonomic Nervous System • Sympathetic Division – Flight or fight response • Parasympathetic Division – Rest or digest response
Brain
The Brainstem • The Medulla Oblongata and the Pons controls breathing, heart rate, digestion • The Cerebellum controls coordination of movement and balance
The Midbrain • The Midbrain receives, integrates, and projects sensory information to the forebrain
The Diencepholon • Forebrain – Epithalamus • Includes the pineal gland the choroid plexus – Thalamus • conducts information to specific areas of cerebrum – Hypothalamus • produces hormones and regulates body temperature, hunger, thirst, sexual response, circadian rhythms
The Telencepholon • Cerebrum – with cortex and corpus callosum • higher thinking
Cerebrum
Cerebrum
Cerebrum
Limbic System • Regulates emotions – Association with different situations is done mostly in the prefrontal lobe
Memory • Short Term – Done in the frontal lobe • Long Term – Frontal lobes interact with the hippocampus and the amygdala to consolidate
Sensory Receptors • • • Mechanoreceptors Pain Receptors Thermoreceptors Chemoreceptors Electromagnetic Receptors
Sensory Receptors • Mechanoreceptors • Pain Receptors • Thermoreceptors
Sensory Receptors • Chemoreceptors
Sensory Receptors • Electromagnetic receptors
Evolution of the Eye • Complex eyes have developed many times
Evolution of the Eye • All light-sensitive organs rely on photoreceptor systems employing a family of proteins called opsins. Further, the genetic toolkit for positioning eyes is common to all animals: the PAX 6 gene controls where the eye develops in organisms ranging from mice to humans to fruit flies
Photoreceptors • Eye cups (ocelli) - light detection • Genetic basis that started as a light detector 600 mya • During the Cambrian explosion around 540 mya two types of eyes arose
Photoreceptors • Compound Eyes made up of ommatidia that helps detect movement
Photoreceptors • Camera Type Eyes – Evolved several times – Hagfish eye – Lamprey eye – Jawed vertebrate eyes
Single Lens Eye • • Sclera (white) Cornea (clear) Choroid (pigmented) Iris (color of eye) Retina (rods and cones) Pupil Fovea (focal point) Blind spot
Photoreceptors Scars of Evolution 1. inside out retina that forces light to pass through the cell bodies and nerves before hitting the retina 2. blood vessels across the retina that cause shadows 3. nerve fibers that exit causing a blind spot
Focusing • Near vision – ciliary muscle contracted – lens becomes more spherical • Distance vision – ciliary muscle relaxed – lens becomes flatter
Visual Problems • Near-sightedness (myopia) – eyeball too long / focal point in front of fovea • Far-sightedness (hyperopia) – eyeball too short / focal point behind fovea • Astigmatism (blurred vision) – misshapen lens or cornea
Hearing and Equilibrium
Hearing Organ • Outer Ear – pinna and the auditory canal – tympanic membrane • Middle Ear – malleus, incus and stapes – oval window • Inner Ear – cochlea with the Organ of Corti • with a basilar membrane and hair cells • Eustachian Tube
Sound • Volume – amplitude of sound wave – vibrates fluid in ear and bend hair cells which generates more action potentials • Pitch – frequency of sound wave
Equilibrium • Utricle and Saccule • Semicircular Canals – used to detect body position and movement
Lateral Line System • Similar to inner ear • detects movement of current, moving objects
Statocysts • Equilibrium • contain statoliths
Sound Systems in Invertebrates • Body hairs that vibrate – mosquitoes • Tympanic Membranes – crickets
Chemoreception • Taste Buds – sweet (tip), salty (behind), sour (sides), bitter (back of tongue)
Chemoreception • Olfactory receptors cells – upper portion of nasal cavity
The Cost of Locomotion
The Cost of Locomotion • Locomotion must overcome two forces: – gravity – friction • Swimming is more efficient than running – runner must overcome gravity • Larger animals travel more efficiently than smaller animals • Flight is the most costly (per minute)
Skeletal Structures • Hydrostatic Skeleton – (cnidaria, ctenophora, platyhelminthes, nematoda, annelida) • Exoskeletons – mollusca, arthropoda • Endoskeletons – chordata
Cooperation of Muscles and Skeletons • Muscles always contract • Muscles attached in antagonistic pairs
Skeletal Muscles • Muscles are made up of muscle fibers • Fibers are made up of myofibrils • Myofibrils are made up of myofilaments – thin filaments (actin) – thick filaments (myosin)
Sliding Filament Model • Sacromeres (basic functioning unit) – Z lines (border of sacromeres) – H zone (center of sacromere) – I band (only thin filaments) – A band (length of thick filaments)
Sliding Filament Model • During contraction, thin and thick filaments slide past each other – I band H zone decreases in size • Caused by myosin head creating cross bridge with actin fiber and then moves by using ATP
Muscle Control • Tropomyosin blocks myosin binding sites • Calcium ions allow cross bridges to form
Muscle Fibers • Fast Muscle Fibers • Slow Muscle Fibers – rapid, powerful contractions – flight muscle – sustain, long contractions – adductor muscles
Invertebrate Muscles • Flight muscles in insects are capable of independent contractions – wings beat faster than action potentials • Clam muscles contain paramyosin that allows them to remain contracted with little energy • Nematodes only have longitudinal muscle that gives them their characteristic movements
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